Background: The aim of the present study was to evaluate the efficacy and safety of 4-week chemotherapy with 5-Fluorouracil (5-FU) and leucovorin (LV) during the resting periods between preoperative chemoradiotherapy (CRT) and surgery in patients with locally advanced rectal cancer (LARC). Methods: Standard preoperative CRT was delivered to the entire pelvis at a total dose of 5040 Gy of radiation with concurrent 5-FU or capecitabine for 6 weeks. Twenty-three patients received additional preoperative chemotherapy with two cycles of 5-FU and LV (LV 200 mg/m² and 5-FU bolus 400 mg/m²on day 1, and 5-FU infusion 2400 mg/m² for 46 hrs, every 2 weeks) after preoperative CRT. Surgery was performed at 2–4 weeks following the completion of preoperative chemotherapy. Results: Between May 2013 and January 2015, 23 patients underwent preoperative CRT, with additional chemotherapy and surgery, and 23 patients completed the scheduled treatment. The median follow-up duration was 42.0 months. The tumor down-staging rate was observed in 65.2%, and pathologic complete remission (pCR) was noted in 5 patients (21.7%). T and N down-staging were observed in 16 (69.6%) and 14 (60.9%) patients, respectively. The four-year disease-free survival (DFS) rate was 73.9% and the four-year overall survival (OS) rate was 90.9% in patients who received additional chemotherapy. The four-year DFS rate was 100% in the tumor down-staging group vs. 25.0% in the non-down staging group treated with additional chemotherapy (P < 0.001). There was also a significant difference of the four-year OS rate 100% in the tumor down-staging group compared with 71.4% in the non-down staging group (P = 0.031). Conclusions: The present study showed that additional preoperative chemotherapy with 5-FU and LV during the resting period after 6-week preoperative CRT is tolerable and active and favorably compares with conventional preoperative CRT. We showed a significant improvement in the four-year DFS and four-year OS rates in the tumor down-staging group.